The Thai island of Koh Samui is a bucket list destination for many and also sees many a traveller returning to its beautiful beaches year after year. Though predicting weather is never an exact science and conditions vary from year to year, there are definitely certain patterns which can help you determine the best time to visit this gorgeous island. Our month-by-month guide to weather in Koh Samui is here to help you decide when to travel.

If you’re trying to decide between different islands, it’s important to note that weather patterns vary drastically between different parts of Thailand and one guide most certainly does not fit all. If you’re trying to decide between Koh Samui and Phuket, check out our post comparing the two islands and have a look at our guide to weather in Phuket.


January is a great time to visit Koh Samui, not just because you get to extended your New Year’s celebrations on the island. With the rainy season drawing to a close, January sees around seven rainy days on average compared to the 15 days you’ll see in October and November. The rain mostly falls during the evenings and overnight. The average temperature hovers around 26°c, making January the “coldest” month of the year on Samui standards – the monthly low is at a chilly 24°c! The weather is very pleasant and the seas are calm too, so it’s a great time to visit if you want to do some snorkelling.


In February, weather in Koh Samui is arguably at its best. There are just five rainy days on average (and again, the showers tend to fall during the night) and when measuring rainfall, this is actually the driest month of the year with an average rainfall of just 30 millimetres. The average temperature remains at a pleasant 27°c. This is also the perfect time to hit the beach with the sea water at a balmy 28°c. As Samui gets a lot of sunshine this time of year, UV index is also at a high 12 so remember to slip, slop and slap when out and about on the island.


Weather in March is quite similar to that in February though it’s getting hotter, with the average temperature climbing up to 28°c. Like the previous month, March sees only the occasional rain shower, mostly falling during the night on an average of four days a month. If you can handle the heat (the average monthly high is a toasty 30°c) and want to return home with a killer tan, March is a great time to visit Koh Samui. Just don’t forget the sunscreen!


In April, the average temperature surges to a scorching 29°c, hitting a high of over 32°c. There are still just five rainy days on average and plenty of sunshine to keep beach goers happy. April is the also the month when Songran or the Thai New Year takes place – nothing like a massive water fight to cool you off in the tropical heat! Though definitely not a Thai holiday, it’s good to note that the Easter holidays might affect pricing and the required minimum stays in Koh Samui villas and resorts.


May is another hot month in Koh Samui, though the increasing rain showers help cool things down a bit. The monthly average is still around 30°c but rain falls on nine days on average. Don’t let the rain put you off though as it seriously helps the whole island feel fresher. May is something of a schizophrenic month as the beginning of the month closely resembles April while late May already sees the island slipping towards rougher weather. The Koh Samui Regatta takes place in May so this might be the perfect time to rent a fabulous yacht.


In June, the weather in Koh Samui is fabulous. After rainy May, the average rainfall drops from over 160 millimetres to just 100 millimetres, with showers falling on an average of nine days. The average temperature still hovers at a steady 29°c. As the school holidays are not in full swing yet, the island is not yet dominated by families which is something you’ll definitely see later in July and August. Overall, June is a fabulous time to visit Koh Samui.


July is one of the most popular times to visit Koh Samui and with good reason. While the weather is starting to get a bit cloudier, you’ll still get plenty of sunshine (around six hours per day), with an average temperature of 29°c. Rain still falls on nine days on average and the monthly rainfall is slightly higher than that in June. With the school holidays in session, the island tends to be very popular with families this time of year.


Like July, August is a busy time in Koh Samui, with lots of families heading in for the school holidays. The weather too is very similar to July with the average temperature steady at 29°c and rain falling on nine days on average. The sea water is an ideal 28°c and the waters on the popular east coast tend to be calm so it’s a great time to head to the beach with the family.


In September, weather in Koh Samui starts cooling down a bit though this is of course relative – the monthly average is still 28°c. Rain falls on an average of 11 days during the month and the rainfall is slightly higher than that in August. That being said, September weather tends to be just as nice as August and since the crowds have already dispersed, you’ll have many parts of the island to yourself.


October is another schizophrenic month in Koh Samui. The beginning of the month tends to be quite sunny, but heading towards the end of the month, weather in Koh Samui really starts gearing towards the rainy season. The monthly rainfall doubles from that in September and you can expect an average of 300 millimetres to fall over some 16 days. That being said, you can still expect temperatures to be around 27°c. Since late October marks the beginning of the dreaded rainy season in Koh Samui, you can expect beaches, restaurants, hotels and villas to be more quiet.


November is typically the rainiest month of the year in Koh Samui. Rain tends to fall on around 15-20 days of the month, with an average monthly rainfall of over 400 millimetres (compared to just 30 mills in the dry month of February). Though rainy season in the tropics might not sound that appealing, you shouldn’t necessarily write November off all together. Though rainy, the month also sees sunny days and since this is the low season, you’re most likely to score some amazing deals with flights and accommodation.

Koh Samui Rainy Beach


Like everywhere else in the world, December is considered peak season in Koh Samui and as the holiday makers start to descend around Christmas, the weather tends to perk up, too. While the most dramatic monsoon rains should be over by now, weather in December can be moody and you shouldn’t bank on having a zero-rain Christmas or New Year. Rainfall drops from +400 to just 150 millimetres and you can expect showers on around nine days. The average temperature is 27°c and this being peak season, prices are at their all-year highest. If you’re planning to stay in Koh Samui during the end of the year holidays, it’s also important to note that most villas require a minimum stay of around 10 nights during the peak dates.

Featured image: Baan Tawantok Estate

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